1. Field of the Invention
The present disclosure relates to a liquid crystal display (LCD) device, and particularly, to an LCD device including a thin film transistor (TFT) compensation circuit in a structure where a driving circuit is implemented by an oxide TFT, the LCD device capable of compensating for degraded characteristics of the TFT due to threshold voltage shift.
2. Background of the Invention
With development of information electronic devices including various types of portable devices such as a mobile phone and a notebook computer, an HDTV, etc. for implementing images of high resolution and high quality, demands for flat panel display devices applied thereto increase. Such flat panel display devices include LCD(Liquid Crystal Display), PDP(Plasma Display Panel), FED(Field Emission Display), OLED(Organic Light Emitting Diodes), etc. However, among such flat panel display devices, the LCD devices are spotlighted because of characteristics of massive production, easy driving, high quality, and a large screen.
Especially, an active matrix-type LCD device where a thin film transistor (TFT) is used as a switching device, is suitable for displaying moving images.
FIG. 1 is a view schematically showing part of an active matrix-type liquid crystal display (LCD) device in accordance with the conventional art. The active matrix-type LCD device includes an LC panel 1 for displaying images. The LC panel 1 is provided with a plurality of gate lines (GL1˜GLn), a plurality of data lines (DL1˜DLm) crossing the gate lines, a switching device (thin film transistor, T) formed at each crossing point, and a pixel (PX) connected to the switching device. Under such configuration, the LC panel 1 is configured to conduct the switching device (T) by a gate driving voltage supplied from the gate lines (GL1˜GLn), and to display images by applying a data voltage to the pixel (PX) through the data lines (DL1˜DLm).
As shown in FIG. 1, the conventional LCD device has a structure where a single gate line and a single data line are allocated to each switching device (T), and pixels included in a single horizontal line are driven for 1 horizontal period (1H). However, as the LC panel 1 has a large area and high resolution, the number of the gate lines (GL1˜GLn) and the data lines (DL1˜DLm) increases. This may increase the number of ICs for supplying a gate driving voltage and a data driving voltage to each line, resulting in increase of the fabrication costs.
In order to solve such problem, an LCD device having a double rate driving (DRD) structure and a MUX structure has been proposed. According to the DRD structure, neighboring switching devices (T) share data lines (DL1˜DLm), so that the number of lines and data driving units is reduced. According to the MUX structure, a prescribed number of data lines adjacent to each other are grouped by a multiplexer (MUX) to thus selectively drive the data lines. This can reduce the number of data driving units to thereby reduce the fabrication costs.
FIG. 2 is a view showing part of an LCD device to which a MUX structure has been applied.
As shown, the LCD device having a MUX structure includes an LC panel 14 having an active area (A/A) for displaying images, and a non-active area (N/A) disposed at an outer side of the active area (A/A). A plurality of gate lines (GL1˜GLn) and data lines (DL1˜DLm) cross each other on the active area of the LC panel 10. A thin film transistor (T) serving as a switching device and a pixel (PX) connected to the switching device are provided at each crossing point.
Data lines (DL1˜DL3) sorted as a group in three, and a single link line (LL) connected to a data driving unit (not shown) are connected to each other through first to third M transistors (MT1˜MT3), respectively, on the non-active area (N/A). The first to third M transistors (MT1˜MT3) are sequentially turned-on, for a first horizontal period (1H), by a MUX controller (not shown) mounted at a timing controller. As a result, a data voltage for three data lines (DL1˜DL3) can be output from output terminals of a single data driving unit.
In the LCD device having a MUX structure, pixels are charged for a period of ⅓H obtained by dividing one horizontal period (1H) into three. Such conventional structure has a difficulty in being applied to an LCD device having a general amorphous silicon TFT having a low current characteristic due to a short pixel charging period. Rather, the conventional structure is applied to an LCD device using an oxide silicon or poly silicon TFT having a high current characteristic.
The oxide TFT has a high current characteristic. However, if a DC voltage is continuously applied to the gate, a device characteristic may be lowered by the degraded TFT due to threshold voltage shift.